Screw press extractor



I June 21, 1966 J, UN- 3,256,808

SCREW PRESS EXTRACTOR Filed June 1, 1964 INVENTOR. APT/4UP HUNT ATTORNEYS United States Patent 3,256,808 SCREW PRESS EXTRACTOR Arthur J.Hunt, 332 N. Halifax Drive,

. ()rmond Beach, Fla. Filed June 1, 1964, Ser. No. 371,624 6 (Ilaims.(Cl. 100-117) This application a continuation-in-part of my copendingapplication Serial No. 285,109 filed June 3, 1963, now Patent No.3,135,193. 7

This invention relates to screw press extractors and more particularlyto a novel and improved screw press particularly adapted for use inextracting liquid from a slurry of wood pulp and liquid in acontinuous-flow pulping process.

In the processing of wood chips to pulp, the chips are placed in adigester which is a large vessel containing a solution referred to ascooking liquor. The pulp and cooking liquor are then heated underpressure in. order to remove resins and gums from the chips and todissolve the lignin which holds together the desired cellulose fibers inthe wood. In one process of digesting pulp, a batch method is usedwherein the digester is. a relatively large vessel, and wherein after apredetermined length of cocking time, the contents of the digester aredischarged into another vessel at atmospheric pressure, this latter stepbeing referred to as blowing. In another process, referred to as acontinuous-flow digester system, the chips are continuously passedthrough a digester containing cooking liquor and under a steam pressureof at least 150 to 175 p.s.i. In either method of digesting'wood pulp,it is important to preserve the cooking liquor inasmuch as it isrelatively expensive and may be reused after suitable processing. In thecontinuous-flow method, the vessel receiving the continuous discharge ofpulp and liquor and/or the means for conveying the-wet pulp to a secondvessel for washing must be such that it will not result in a substantialbleeding of pressure from the digester as this would adversely affectthe economics of the cooking cycle.

The pulp as it is discharged from either a batch or continuous-flowdigester contains up to 96 to 97 percent, by weight, of cooking liquor.As previously noted it is important to recover the liquor for reuse, andfurther, it it necessary to remove the same from the pulp prior tosubsequent operations in the manufacture ofpaper. This may beaccomplished by passing the saturated pulp through rollers, whereby thepulp is compressed to remove at least a portion of the liquor therefrom.In pressing the pulp it is important that it be compressed suflicientlyto remove the maximum amount of liquor therefrom without compressing itsufficiently to crush the cellulose fibers together to form paper; forexample, the pulp might be pressed until it had approximately 25percent, by weight, of liquid remaining therein.

This invention contemplates using a screw press for effecting the abovedescribed extracting step. Such a screw press might comprise anelongated, rotatable worm or screw fitting within a foraminate sleevewhich in turn is contained within a housing forming means for collectingliquid passing through the screen. Liquid tends to pass through thescreen while solids are carried longitudinally of the screen by therotating screw. The crosssectional area of the passageway or channeldefined by the screw thread or rib diminishes from the inlet end of thescreen toward the outlet end thereof whereby the solids collected arecompacted or compressed to extract liquid contained therein, with theliquid passing through the screen and into the collection means formedby the housing. Where, among other reasons, the solids being separatedhave a characteristic of tending to adhere to adjacent surfaces, theremay be a tendency of the solids 3,256,808 Patented June 21, 1966 to clogthe screen and prevent efiicient flow of liquid therethrough. This istrue where a slurry of liquid and wood pulp is being passed through theextractor.

Accordingly it is one of the primary objects of this invention toprovide a novel and improved extractor of the screw press type forseparating liquids and solids from a slurry thereof, or from solidscontaining a relatively large percentage of liquid, and which willsubstantially eliminate any tendency of the screen to clog with solidsso as to impair significantly the flow of liquid from the extractor.

It is a further object of this invention to provide a novel and improvedextractor of the type described which is particularly adapted forextracting liquid from wood pulp and which will provide a satisfactoryreduction in liquid content of the pulp without compacting the samesufficiently to form paper or otherwise adversely aiiect subsequentoperation on the pulp.

Included within the last mentioned object, is the object of providingsuch an extractor which is particularly adapted for use in combinationwith a continuous-flow digester, whereby the extractor may be connectedto receive pulp directly from the digester without causing a significantbleed of pressure from the digester.

In accordance with one aspect of the invention a screw press is providedwhich is adapted to receive material at an. inlet pressure of, forexample, up to at least p.s.i., which will extract liquid from thesolids contained within the material and discharge the liquid at apressure not substantially less than the inlet liquid pressure While atthe same time will discharge the solids to atmospheric presure. Theextractor comprises an elongated screw fitting closely within a seriesof cylindrical members including a pair of imperforate cylindricalmembers at either end of the screw. A foraminate cylindrical mem her isdisposed intermediate the ends of the screw and is contained within ahousing forming means for collecting liquid extracted from the materialbeing processed. The extractor extends at a substantial angle to thehorizontal and has an inlet opening disposed between the ends of theimperforate cylindrical member at the inlet end of the screw and anoutlet in said housing registering with a point intermediate the ends ofsaid screen. The screw and cylindrical members'cooperate to form ahelical passage extending longitudinally of the screw axis. Thecrossasectional area of this passage decreases very gradually from theinlet end of the screw to the outlet end thereof. A valve is provided inthe outlet passage to maintain the pressure drop across the extractorsufiiciently small that there will not be a significant adverse bleed ofpressure [from the pressure vessel from which the material is being fedto the inlet of the extractor. Also, this valve, as well as the speed ofrotation of the screw, controls the outlet flow of liquid, so that theliquid level within the extractor is maintained substantially above theoutlet, with the result that the solids are maintained in a liquid overa substantial portion of the screen length. This prevents the solidsfrom clogging the screen below the liquid level in the extractor andparticularly adjacent the liquid outlet. liquid level in the extractortoward the outlet end, wherein is provided means for tending to obstructthe flow of solids from the outlet end of the helical passage throughthe extractor. Such obstruction means are adjustable to provide apredetermined back pressure at the outlet end of the extractor, wherebysolids will build up for a substantial length from the outlet end of theextractor toward the inlet end thereof forming a relatively solid packof material preventing the escape of pressure from this end of theextractor and in another aspect of the invention acting as a journal orbushing for the outer end of the screw. Y

The screw carries solids above the The novel features which are believedto be characteristic of this invention are set forth with particularityin the appended claims. The invention itself, however, both as to itsorganization and method of operation, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawing, in which:

FIG. 1 is a side elevational view of an extractor incorporating thepresent invention with parts removed for clarity;

FIG. 2 is an end view of the extractor of FIG. 1, as

I indicated by the line 22 of FIG. 1;

FIG. 3 is an enlarged, longitudinal cross-sectional view of theextractor substantially along line 33 of FIG. 2;

and

FIG. 4 is an enlarged, cross-sectional view substantially along the line44 of FIG. 3.

With reference to the drawing, and particularly FIGS. l3 thereof, anextractor incorporating the present in vention is generally indicated at10. As shown in FIG. 1 the extractor extends at a substantial angle tothe horiz-ontal, being supported by frames or standards 12 and 14adjacent the inlet and outlet ends, respectively, of the extractor. Asmost clearly shown in FIG. 3, the extractor comprises the housing,generally indicated at 16, including a pair of coaxially disposedcylindrical, imperforate members 18 and 20. The cylindrical members 18and 20 have flanges 22 and 24, respectively, at their next adjacent endswhich are joined in fluid tight relation. Disposed concentrically withinthe cylindrical member 20 is a cylindrical, imperforate member 26 whichis spaced radially inwardly from the member 20 and is joined in fluidtight relation at one end to the flange 24. The ends of the cylinders 20and 26 opposite the flange 24 are closed by an end plate 28 on which ismounted a bracket 30 to which the standard 12 is connected. An inletconduit 32 extends radially outwardly from the cylinder 26 intermediatethe ends of the cylinder and through the cylinder 20 for connection to asource of material to be fed into the extractor.

The end of the cylinder 18 opposite the flange 22 terminates in aradially inwardly extending flange 34 which is secured in fluid tightrelation with a radially outwardly extending flange 36 at one end of acylindrical imperforate member 38 extending coaxially of the cylinder18. It will thus be seen that the housing is provided with an elongate,cylindrical bore having a central portion formed by the cylinder 18 anda pair of reduced diameter portions at either end of the central portionformed by the cylinders 26 and 33.

Disposed within the central portion of the housing is a foraminate,cylindrical sleeve 40 extending coaxially of and disposed within thecylinder 18 in radially inwardly spaced relation. The sleeve 40 is fixedrelative to the cylinder 18, such as by Welding the ends of the sleeveto the flanges 22 and 34. Disposed within and lining the sleeve 40 is agenerally cylindrical screen 42 which has an inner surface generallyproviding a continuation of the cylindrical surfaces of the cylinders 26and 38 which have equal inner diameters. The screen 42 has openingssubstantially smaller than those of the sleeve 40 with the screen 42providing control of the size of the solids which may pass through thesleeve 40 into the liquid collection space between the sleeve andcylinder 18. The screen 42 is relatively flexible while the sleeve 40 isrelatively rigid so as to provide support for the screen duringoperation of the apparatus. A liquid outlet conduit 41 is provided whichcommunicates at its inner end with the space between the cylinder 13 andsleeve 40 and is located between the ends 'of the cylinder 18 moreclosely adjacent the flange 22 than the flange 34.

Disposed concentrically within the substantially constant diameter,cylindrical passage formed by the cylinders 26 and 38 and the screen 42is a screw, generally indicated at 44. The screw comprises a shaft orshank, generally indicated at 46, and extending coaxially of thehousing. The inlet end of the shaft extends outwardly through a rotatingseal 48 carried by the end plate 28 and through a bearing 50 carried bythe bracket 30. The outer end of the shaft, as is shown in FIG. 2, isdrivingly connected, such as by belt or chain and sprocket drive, to anelectric motor 52 supported by the standard 12.

The screw shank 46 comprises a first portion 54 extending from nextadjacent the end plate 28 to a point intermediate the ends of the screen42 whereat it terminates in a reversely-tapered, frusto-conical secondportion 56. The portion 56 of the shank terminates adjacent the flange34 in a cylindrical third portion 53. All portions of the shaft arespaced radially inwardly from the inner diameter of the surroundingcylindrical members. The screw further comprises a helical rib 60extending from next adjacent the inlet end of the screw to the nextadjacent the outlet end thereof. The outer diameter of the screw issubstantially constant over the entire length of the rib 60, and the ribouter diameter is disposed closely adjacent, if not engaged with, theinner surfaces of the next adjacent surrounding cylindrical members.

From a consideration of FIG. 3 it will be observed that the screw incooperation with the next adjacent surrounding cylindrical members formsa helical passage extending from the inlet end of the screw to theoutlet end thereof. It will also be observed that the cross-sectionalarea of this passage diminishes over the screw length from the inlet endtoward the outlet end. This reduction in crosssectional area of thepassage is accomplished both by a decrease in the pitch of the rib 60from the inlet to the outlet end of the screw, as well as by an increasein the outer diameter of the shank 46 of the screw over thefrusto-conical portion 56 thereof. Where the extractor is used inconnection with the removal of liquid from wood pulp the reduction incross-sectional area of the helical passage should be relatively small,on the order of four to one, between the inlet and outlet end of thehelical passage, and on the order of about three to one between theinlet end of the helical passage and the greater diameter end of thefrusto-conical portion 56 of the shank. Also the pitch change of the ribshould be quite gradual and the total decrease in pitch over the lengthof the screw relatively small. For example, in a practical design of theinvention intended to be used for extracting liquid from wood pulp, andwherein the screw had an outer diameter of 4 inches and a length ofabout 5 feet the pitch at the inlet end of the screw was approximately 4inches, while the pitch at the outlet end of the screw was approximately3 inches. In this design, the frustoconical portion 56 of the shank wasapproximately 1% feet long and had a lesser diameter at one end of about2 inches and a greater diameter at the other end of about 3% incheswhereby providing an included angle of approximately 9 degrees. Thepitch of the rib decreased only slightly between the inlet end of thescreen 42 and the lesser diameter of the frusto-conical portion 56.

Thereafter the pitch decreased from about 3% inches to slightly lessthan 3 inches at the outlet end of the screen which is approximately atthe greater diameter end of the frusto-conical portion 56 of the shank.Thus, it can be seen that the cross-sectional area of the channel de--creased very gradually. The rib extended about 16 turns with thegreatest rate of change in cross-sectional area of the helical passageoccurring over the frusto-conical portion 56 of the screw shank. In thisarea the channel cross-sectional area decreased in the ratio of about 3to 1, or slightly less, and from the greater diameter of thefrusto-conical portion to the outlet end of the screw decreased on theorder of 1.25: 1.

In using the apparatus of this invention to remove liquid from materialfed directly from a vessel under pressure, such as a continuous-flowwood pulp digester, the inlet conduit 32 is connected to the vessel. Avalve 62 is provided in the liquid outlet conduit 41 to maintain a smallpressure drop across the extractor suflicient to permit the flow ofliquid therethrough but insufiicient to adversely bleed pressure fromthe vessel supplying the inlet 32. The material supplied may be in theform of a slurry comprising liquid and pulp containing a high percentageof liquid, for example, on the order of 97 percent by weight of liquid.The mixture is fed into the chamber defined by the cylindrical member 26and rotation of the screw tends to feed the solids in the mixture towardthe outlet end of the screw. The liquid in the extractor will extendvertically to a level, generally indicated in FIGS. 1 and 3 at 64,substantially above the outlet 41. The maintenance of the liquid levelsubstantially above the liquid outlet 41 assures that the solids in theextractor below this point will be relatively free and uncompacted andwill not clog the screen 42. The imperforate cylindrical member 26prevents any flow of liquid outwardly from the inlet end of theextractor housing and assures that solids at the inlet end are submergedin liquid. Rotation of the screw keeps the solids in suspension in theliquid and prevents the solids from settling to the lower end of theextractor, thus preventing clogging of the inlet conduit. The solidswill be collected on the rib 60 and carried above the liquid level 64where they will be compressed in the area of the extractor correspondingto the frusto-conical portion of the shank to remove liquid therefrom.The extracted liquid will flow through the screen 42 into the spacebetween the sleeve 40 and cylinder 18 and thence to the outlet '41. Thesolids pass from the greater diameter end of the frusto conical shank 56into the channel defined in part bythe cylinder 38 where they arefurther compacted but to a lesser degree.

The discharge of solids from the outlet end of the passage formed inpart by the screw is impeded by means at the discharge end of thechannel in a manner to cause the solids to be relatively firmly packedto form a plug extending from the outlet endof the helical passagetoward the inlet end of the screw and substantially to the inlet end ofthe cylinder 38. This plug of material serves to seal the outlet end ofthe apparatus to prevent the escape of pressure therefrom. Also thisplug acts as a journal or bushing for the outer end of the screw shank,

which it will be noted is otherwise unsupported except as provided byany contact between the outer diameter of the rib and the inner diameterof the cylinder 38.

In the specific embodiment shown, the means for obstructing the flow ofsolids from the outlet end of the screw comprises a member or flipper 66which, as shown in FIG. 3, is disposed between the last and the next tolast turn of the screw rib 60. The flipper 66 fits closely within anopening in the screw shank and has a leading edge remote from the outletend of the screw passage. The leading edge of the flipper has an outersurface forming a continuation of the next adjacent outer surf-ace ofthe screw shank. The leading edge portion of the flipper is, as is shownin FIG. 4, pivotally mounted as at 68 on the screw shank for movement ofthe other or trailing edge of the flipper outwardly and inwardly of theshank. In the specific embodiment shown, means are provided forresiliently and yieldably urging the flipper outwardly of the shank.Such means comprises a compression coil spring 70 telescopicallydisposed at one end over a post 72 fixedly mounted on a stub shaft 74carried by a disc 76 disposed concentrically within and fixed to thetubular outer end of the screw shank 46. The post 72 extends radially ofthe shaft 74 which is disposed coaxially of the screw shank. A pair ofnuts, as at 78, are threadably mounted on the post 72. The other end ofthe spring is disposed over a post similar to the post 72 carried by theunderside of the flipper 66 and extending inwardly of the screw axis. Itwill be apparent that by outward threading of the nuts 78 thecompression of the spring 70 may be adjusted to provide a predeterminedforce on the underside of the flipper urging the same away from thescrew shank and toward the inner diameter of. thesleeve 38.

The force exerted by the spring 70 on the flipper 66 will determine theback pressure imparted on the solids discharging from the extractor.This back pressure must be sufiicient to prevent blowout of the plug atthe outer end of the screw so as to maintain the desired pressure withinthe extractor. In this connection the flipper 66 should fit closelybetween the last and next to last turn of the rib 60. In order to avoidloss of pressure in the vessel feeding the extractor, during initialstartup of the apparatus and until such time as the plug of solids isobtained as aforedescribed, it may be desirable to provide sealing meanson the edges of the flipper to provide an effective pressure seal.

In the use of the extractor to remove liquid from wood pulp, it ispreferred that the amount of liquid in the solid material dischargedfrom the extractor be no less than about 25 percent by weight of thematerial. The pulp is compressed only very slightly between the inletend of the screw and the lesser diameter end of the frustoconicalportion of the screw shank. In this connection the cross-sectional areaof the helical passage defined in part by 'the screw, as well as thepitch of the screw remains substantially constant from the inlet end ofthe screw to the inlet end of the screen 42. At least about 3 turns ofthe screw rib are disposed in the cylinder 26 to assure proper agitationof the solids in suspension to prevent clogging of the inlet. Thus, itwill be seen that little, if any, compression of the pulp occurs belowthe lesser diameter end of the portion 56 of the screw shank whichcorresponds generally to the liquid level in the extractor. Over thescrew shank portion 56, the cross-sectional area of the helical passageis gradually reduced both by the increasing outer diameter of the shankand a decrease in pitch of the rib 60. The cross-sectional area of thehelical passage at the inlet and outlet ends, respectively, of the shankportion 56 should be in a ratio of about 3:1. In the portion of thehelical passage contained within the cylinder 38, the cross-sectionalarea reduction of the passage should be about 1.25 :1 from the inner tothe outer end of the cylinder by reason of a further decrease in pitchof the rib. It will thus be seen that substantially all of thecompression of the pulp occurs over the shank portion 56 above theliquid level. After the pulp passes from the extractor it may drop intoa collection bin or tank, preferably filled with fresh water andprovided with agitating means to break up the pulp so that it may morereadily absorb the fresh water for further rinsing operations. The pressmay be operated relatively fast, on the order of at least 125 rpm. Thepulp is gradually compressed in the extractor to remove a sufiicientquantity of liquid therefromwhile at the same time not compactedsufficiently to form paper. Further, the structure of the extractorassures that neither the inlet 32 nor the screen 42 will become cloggedwith pulp thus interfering with the continuous flow of liquid from theinlet 32 through the outlet 41. Thus, it can be seen that a screw pressof the present invention is readily adapted to a continuous digestingoperation.

While the invention thus far has been described primarily in connectionwith the washing of pulp in a convolume of the garbage were reduced to25 or 50 percent of the original weight or volume there would be asizable economy realized. Where the extractor is used for such a purposeit would not be necessary to provide a sealing plug at the outer end ofthe extractor; rather the flipper 66 would merely be used, if at all, tomaintain sufiicient back pressure on the solid material being dischargedto assure suflicient extraction of liquid therefrom. Further, the valve62 in the outlet conduit 41 would not be required as it would not benecessary to maintain pressure within the system. However the valvecould be used to assist in maintaining the liquid level 64 at the heightdescribed previously in order to assure that there will be noclogging'of the screen 42. The imperforate cylindrical member 26 wouldoffer advantages in this last connection, in that it would assure thatthe garbage at the inlet end of the screw would be maintained insuspension in liquid so as not to be compacted and clog the inlet 32.

While only certain preferred embodiments of this invention have beenshown and described by way of illustration, many modifications willoccur to those skilled in the art and it is, therefore, desired that itbe understood that it is intended in the appended claims to cover allsuch modifications as fall within the true spirit and scope of thisinvention.

What is claimed as new and what it is desired to secure by LettersPatent of the United States is:

'1. In a system for extracting liquid from solids containing liquid, ascrew press comprising a rotatable screw having its axis extending at asubstantial angle to the horizontal, foraminate means surrounding saidscrew intermediate its ends and disposed closely adjacent to the outerdiameter of said screw, means providing an impertforate housing having afirst portion surrounding said fora minate means in outwardly spacedrelation and a second portion surrounding the lower end of said screw inclosely adjacent relation, means providing an inlet in said housingbelow said foraminate means, means providing a liquid outlet in saidhousing intermediate the ends of said'foraminate means, and means formaintaining the liquid level in the extractor above said liquid outlet,said screw cooperating with said'second portion of the housing belowsaid foraminate means and with said foraminate means to provide ahelical passage extending about said screw axis, the cross-sectionalarea of said passage being less adjacent the upper end of saidforaminate means than adjacent the lower end thereof with a substantialmajority of the reduction in said cross-sectional area occurring abovethe liquid outlet of the extract-or, said second portion extending overat least about three turns of said screw to assure that during operationof the press the solids in said second portion Will be suspended inliquid to preclude clogging of said outlet.

2. In a screw press for extracting liquid from a solid containingliquid, a rotatable screw having its axis extending at a substantialangle to the horizontal, means providing a housing surrounding the saidscrew and extending longitudinally thereof, foraminate means surroundingthe screw intermediate its ends and disposed closely adjacent the outerdiameter of said screw, means providing an inlet for said housingadjacent its lower end, means providing a liquid outlet in said housingintermediate the ends of said f-oraminate means, means to maintain theliquid level within said housing substantially above said liquid outlet,said screw in part defining a helical passage extending from the lowerend of the screw to the upper end thereof, the cross-sectional area ofsaid passage being lesser at the upper end of said foraminate means thanat the lower end thereof with a substantial majority of the reduction incross-sectional area of said passage taking place above said liquidlevel, and means for providing a fluid pressure seal to prevent theescape of fiuid pressure from within said housing through the upper endof said helical passage comprising means adjacent the upper end of saidscrew for impeding the flow of material out of said passage.

3. In a screw press for extracting liquid from a solid containingliquid, a rotatable screw having its axis extending at a substantialangle to the horizontal, means providing a housing for said screwcomprising a first imperforate cylindrical member disposed coaxiallyover the lower end of said screw closely adjacent to the outer diameterthereof and extending over a plurality of turns of said screw, meansclosing the lower end of said cylindrical member, a second imperforatecylindrical member extending coaxially of the screw from the upper endof said first cylindrical member in radially outwardly spaced and fluidtight relation thereto, foraminate means disposed within said secondcylindrical member in radially inwardly spaced relation and closelyadjacent the outer diameter of said screw, means providing an inlet insaid first cylindrical member intermediate the ends thereof, meansproviding a liquid outlet in said second cylindrical member intermediatethe ends thereof, and means for maintaining the liquid level in saidhousing above said liquid outlet, said screw forming in cooperation withsaid first cylindrical member and said foraminate means a helicalpassage extending about said screw and longitudinally of its axis, thecross-sectional area of said passage being lesser adjacent the upper endof said foraminate means than adjacent the lower end thereof with agreater amount of reduction in cross-sectional area of said passageoccurring above said liquid level.

4. A screw press for extracting liquid from a solid containing liquidcomprising a rotatable screw having its axis extending at a substantialangle to the horizontal and including a shank having a cylindrical firstportion extending from the lower end of the screw and terminating in areversely tapered frusto-conical second portion which in turn terminatesin a cylindrical third portion of the same diameter as the greaterdiameter end of said second portions of the shank, a helical ribdisposed about said shank and extending longitudinally thereof, said ribhaving a substantial constant outer diameter, the pitch of said ribbeing substantially constant from the lower end thereof to a pointadjacent the lesser diameter end of said second portion of the shank andthen gradually decreasing over said second portion to the greaterdiameter end thereof to a predetermined amount, the pitch of said ribfurther decreasing from adjacent the greater diameter end of said secondportion of the shank to the upper end of said screw but to asubstantially lesser degree than the decrease in pitch over said secondportion, an imperforate first cylindrical member disposed coaxially overthe lower end of said screw and extending over a plurality of turns ofsaid rib from the lower end of the screw, said first member terminatingin an imperforate second cylindrical member disposed coaxially aboutsaid screw in radially outwardly spaced relation, said second memberterminating in an irnperforate third cylindrical member disposedcoaxially about and closely adjacent the outer diameter of said rib andextending at least'to the upper end of said screw, cylindricalforaminate means disposed coaxially within said second member inradially inwardly spaced relation and closely adjacent the outerdiameter of said screw, the inner diameter of said foraminate meansbeing substantially equal to the inner diameters of said first and thirdmembers, valve means connected to said liquid outlet to maintain thepressure drop across said extractor to a predetermined amount, meansincluding said valve means to maintain the liquid level in saidextractor substantially above said liquid outlet and adjacent the lesserdiameter end of said second portion of the shank, and means to preventany substantial leakage of fluid pressure externally of the extractorthrough the upper end of said third member comprising means adjacent theupper end of said third member tending to impede the flow of materialtherefrom thereby to provide a plug of material over a substantiallength of said third member with the plug further tending to provide abearing for the upper end portion of said screw.

5. A screw press as described in claim 4 wherein said last mentionedmeans comprises a flipper disposed between the last and next to lastturn of said rib, said flipper having a leading edge remote from theouter end of said rib which is pivotally supported on said shank formovement of the other end of the flipper toward and away from saidshank, and resiliently yieldable means acting on said flipper andtending to move said other end of the same outwardly of the shank towardthe inner surface of said third cylindrical member.

6. In a screw press for extracting liquid from wood pulp and the like, arotatable screw having its axis extending at a substantial angle to thehorizontal, an imperforate generally cylindrical housing for the screwhaving a center portion spaced outwardly from the screw and terminatingat its ends in a pair of reduced diameter end portions disposed closelyadjacent the outer diameter of the screw, generally cylindricalforaminate means disposed in said outer portion coaxially over the screwin inwardly spaced relation to said center portion and closely adjacentto the outer diameter of the screw, said screw and end portions andforaminate means cooperating to provide a helical passage having asubstantially constant cross-sectional area from the lower end thereofto a point between the ends of said foraminate means, saidcrosssectional area decreasing between said point to the upper end ofsaid screw sufliciently and in a manner to remove a predetermined amountof liquid from wood pulp while not compacting the pulp sufliciently toform paper, means providing an inlet below said foraminate means, meansproviding an outlet between said inlet and said point, means formaintaining the liquid level in said housing above said outlet andadjacent said point, means to prevent escape of fluid pressure withinsaid housing through the upper end of said helical passage includingmeans adjacent the upper end of the upper of said end portions tendingto obstruct flow of solid material from the upper end of said helicalpassage to provide a fluid pressure sealing plug of said solid materialin said helical passage extending over more than one turn of saidpassage about said axis, means to maintain a relatively low pressuredrop between said inlet and outlet, the cross-sectional area of saidpassage being reduced in the ratio of about 3:1 between said point andthe upper end of said foraminate means and to a substantially lesseramount between the upper ends of said foraminate means and the upper endof the screw, said means to prevent escape of fluid pressure beingoperable to effect the maintenance of a fluid pressure within thehousing of at least about 100 psi.

References Cited by the Examiner UNITED STATES PATENTS Sullivan 100-93WALTER A. SCHEEL, Primary Examiner.

LOUIS O. MAASSEL, Examiner.

2. IN A SCREW PRESS FOR EXTRACTING LIQUID FROM A SOLID CONTAINING LIQUID, A ROTATABLE SCREW HAVING ITS AXIS EXTENDING AT A SUBSTANTIAL ANGLE TO THE HORIZONTAL, MEANS PROVIDING A HOUSING SURROUNDING THE SAID SCREW AND EXTENDING LONGITUDINALLY THEREOF, FORAMINATE MEANS SURROUNDING THE SCREW INTERMEDIATE ITS ENDS AND DISPOSED CLOSELY ADJACENT THE OUTER DIAMETER OF SAID SCREW, MEANS PROVIDING AN INLET FOR SAID HOUSING ADJACENT ITS LOWER END, MEANS PROVIDING A LIQUID OUTLET IN SAID HOUSING INTERMEDIATE THE ENDS OF SAID FORAMINATE MEANS, MEANS TO MAINTAIN THE LIQUID LEVEL WITHIN SAID HOUSING SUBSTANTIALLY ABOVE SAID LIQUID OUTLET, SAID SCREW IN PART DEFINING A HELICAL PASSAGE EXTENDING FROM THE LOWER END OF THE SCREW TO THE UPPER END THEREOF, THE CROSS-SECTIONAL AREA OF SAID PASSAGE BEING LESSER AT THE UPPER END OF SAID FORAMINATE MEANS THAN AT THE LOWER END THEREOF WITH A SUBSTANTIAL MAJORITY OF THE REDUCTION IN CROSS-SECTIONAL AREA OF SAID PASSAGE TAKING PLACE ABOVE SAID LIQUID LEVEL, AND MEANS FOR PROVIDING A FLUID PRESSURE SEAL TO PREVENT THE ESCAPE OF FLUID PRESSURE FROM WITHIN SAID HOUSING THROUGH THE UPPER END OF SAID HELICAL PASSAGE COMPRISING MEANS ADJACENT THE UPPER END OF SAID SCREW FOR IMPEDING THE FLOW OF MATERIAL OUT OF SAID PASSAGE. 